Cutting tool insert

ABSTRACT

The present invention relates to a cutting tool insert for side and face milling of rolled low alloyed steel at low and at moderate cutting speeds comprising a cemented carbide body and a coating and a method for making same. The cemented carbide body comprises WC, from about 7.3 to about 7.9 wt-% Co and from about 1.0 to about 1.8 wt-% cubic carbides of Ta and Nb and a highly W-alloyed binder phase with a CW-ratio of from about 0.86 to about 0.94. The coating comprises: 
         a first (innermost) layer of TiC x N y O z  with a thickness of from about 0.1 to about 2 μm, and with equiaxed grains with size less than about 0.5 μm    a layer of TiC x N y O z  with a thickness of from about 2 to about 10 μm with columnar grains with a diameter of about less than about 5 μm    a layer of TiC x N y O z  with a thickness of 0.1-2 μm and with equiaxed or needlelike grains with size less than about 0.5 μm    an outer layer of a smooth, textured, finegrained α-Al 2 O 3  layer with a thickness of from about 2 to about 10 μm. The invention also relates to the use of such a cutting tool insert for side and face milling of rolled low alloyed steel at low and moderate cutting speeds.

BACKGROUND OF THE INVENTION

The present invention relates to a chamfering cutting tool insertparticularly useful for the milling of plates intended for manufacturingof tubes for pipelines for crude oil, natural gas or the like.

Pipelines are frequently used to transport fluid products forsubstantial distances, with oil and gas transmission pipelines being buttwo well-known examples. Such pipelines are generally constructed ofindividual pipe sections that are joined together by welding.

Individual pipe sections are formed from huge plates on the order of 4m×12 m with a thickness of 25 mm, of low alloyed steel and weldedlongitudinally.

Separate lengths of pipe are typically interconnected by electric-arcwelding and many types of welding techniques are used or proposed in theart for that purpose.

The plates are machined to obtain a chamfer suitable for the subsequentwelding of the individual sections as well as the welding together ofseparate pipe sections.

The machining of the plates to obtain the desired character is made inlarge milling machines with cutters having a diameter of from about 600to 1200 mm, provided with 40-80 inserts of rectangular shapetangentially mounted with dimensions of 32×20×8 mm. Normally inserts ofcoated cemented carbide grade tools are used.

It is important to obtain long tool life and minimise the tool changefrequency in order to reduce the cost. The criteria for the operationare sufficient surface finish and little or no structure deformation. Itis important to create a surface finish that does not disturb thewelding process.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a cutting toolinsert particularly useful for the chamfer milling of steel plates foroil pipelines and similar.

In one aspect of the invention, there is provided a cutting tool insertcomprising a cemented carbide body and a coating said cemented carbidebody comprising WC, from about 7.3 to about 7.9 wt-% Co and from about1.0 to about 1.8 wt-% cubic carbides of Ta and Nb, a highly W-alloyedbinder phase with a CW-ratio of from about 0.86 to about 0.94, and anedge radius of from about 20 to about 45 μm, said coating comprising

a first (innermost) layer of TiC_(x)N_(y)O_(z) with a thickness of fromabout 0.1 to about 2 μm, and with equiaxed grains with size less thanabout 0.5 μm

a layer of TiC_(x)N_(y)O_(z) with a thickness of from about 2 to about10 μm with columnar grains with a diameter of less than about 5 μm

a layer of TiC_(x)N_(y)O_(z) with a thickness of from about 0.1 to about2 μm and with equiaxed or needlelike grains with size less than about0.5 μm

an outer layer of a smooth, textured, finegrained α-Al₂O₃ layer with athickness of from about 2 to about 10 μm.

In another aspect of the invention, there is provided a method of makinga cutting tool insert comprising a cemented carbide body and coating thecemented carbide body having a composition of from about 7.3 to about7.9 wt % Co, from about 1.0 to about 1.8 wt % cubic carbides and balanceWC with a content of Ti on a level corresponding to a technicalimpurity, the average grain size of the WC being in the range of fromabout 1.5 to about 2.5 μm, and hardness from about 1500 to about 1600 HVand a CW-ratio of from about 0.84 to about 0.94, and with an edge radiusof from about 20 to about 45 μm comprising coating said body with

a first (innermost) layer of TiC_(x)N_(y)O_(z) with x+y+z=1 with athickness of from about 0.1 to about 2 μm, and with equiaxed grains withsize less than about 0.5 μm using known CVD-methods

a layer of TiC_(x)N_(y)O_(z) with x+y+z=1 with a thickness of from about2 to about 10 μm with columnar grains and with a diameter of about <5μm, deposited either by MTCVD-technique (using acetonitrile as thecarbon and nitrogen source for forming the layer in the temperaturerange of 700-900° C.) or by high temperature CVD-technique (1000-1100°C.), the process conditions being selected to grow layers with columnargrains.

a layer of TiC_(x)N_(y)O_(z) with x+y+z=1 with z<0.5, with a thicknessof from about 0.1 to about 2 μm and with equiaxed or needlelike grainswith size less than about 0.5 μm, using known CVD-methods, this layerbeing the same as or different from the innermost layer.

a layer of a smooth textured α-Al₂O₃ layer with a thickness of fromabout 2 to about 10 μm, and a surface roughness (Ra) of less than about0.3 mm over a measured length of 0.25 mm.

In still another aspect of the invention, there is provided a use of acutting tool insert as described above for side and face milling ofrolled low alloyed steel at low or moderate cutting speeds.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

It has now surprisingly been found that with the present invention anincreased tool life can be obtained.

According to the present invention, coated cutting tool insertsparticularly useful for chamfer milling of steel plates intended for oilpipes are provided comprising a cemented carbide body with a compositionof from about 7.3 to about 7.9 wt % Co, preferably about 7.6 wt % Co,from about 1.0 to about 1.8 wt % cubic carbides, preferably from about1.4 to about 1.7 wt % cubic carbides of the metals Ta and Nb and balanceWC. The content of Ti is preferably on a level corresponding to atechnical impurity. The average grain size of the WC is in the range offrom about 1.5 to 2.5 μm, preferably about 1.8 μm and hardness fromabout 1500 to about 1600 HV.

The cobalt binder phase is rather highly alloyed with W. The content ofW in the binder phase can be expressed as the CW-ratio=Ms/(wt %Co×0.0161), where Ms is the saturation magnetization of the cementedcarbide body in kA/m and wt % Co is the weight percentage of Co in thecemented carbide. The CW-value is a function of the W content in the Cobinder phase. A high CW-value corresponds to a low W-content in thebinder phase.

According to the present invention, an improved cutting performance isachieved if the cemented carbide body has a CW-ratio of from about 0.84to about 0.94 preferably from about 0.86 to about 0.91.

The coating comprises a first (innermost) layer of TiC_(x)N_(y)O_(z)with x+y+z=1, preferably z<0.5, with a thickness of 0.1-2 μm, and withequiaxed grains with size less than about 0.5 μm;

a layer of TiC_(x)N_(y)O_(z) with x+y+z=1, preferably with z=0 and x>0.3and y>0.3, with a thickness of from about 2 to about 10 μm, preferablyfrom about 4 to about 7 μm, with columnar grains and with a diameter ofabout 5 μm, preferably less than about 2 μm;

a layer of TiC_(x)N_(y)O_(z) with x+y+z=1 with z<0.5, preferably z>0.1,with a thickness of from about 0.1 to about 2 μm and with equiaxed orneedlelike grains with size less than or equal to about 0.5 μm, thislayer being the same as or different from the innermost layer;

-   -   an outer layer of a smooth, textured, finegrained (grain size        about 1 μm) α-Al₂O₃ layer with a thickness of from about 2 to        about 10 μm, preferably from about 3 to about 6 μm, and a        surface roughness (Ra) of less than about 0.3 mm over a measured        length of 0.25 mm; and preferably

a further layer of from about 0.5 to about 1.0 μm thick TiN. Thisoutermost layer of TiN has a surface roughness Rmax less than about 0.4μm over a length of 10 μm.

The inserts have before coating an edge radius of from about 20 to about45 μm, preferably about 35 μm. The TiN-layer is reduced in thicknessover the edge line to 50-90% of its thickness on the rake face.

In addition, the α-Al₂O₃ layer has a preferred crystal growthorientation in either the (012)-, (104)- or (110)-direction, preferablyin the (012)-direction, as determined by X-ray Diffraction (XRD)measurements. A Texture Coefficient, TC, is defined as:${{TC}({hkl})} = {\frac{I({hkl})}{I_{o}({hkl})}\left\{ {\frac{1}{n}{\sum\quad\frac{({hkl})}{I_{o}({hkl})}}} \right\}^{- 1}}$whereI(hkl)=measured intensity of the (hkl) reflectionI(hkl)=standard intensity of the ASTM standard powder patterndiffraction datan=number of reflections used in the calculation, (hkl)reflections used are: (012), (104), (110), (113), (024), (116)

According to the invention, the TC for the set of (012), (104) or (110)crystal planes is larger than about 1.3, preferably larger than about1.5.

The invention also relates to a method whereby a cemented carbide bodywith a composition of from about 7.3 to about 7.9 wt % Co, preferablyabout 7.6 wt % Co, from about 1.0 to about 1.8 wt % cubic carbides,preferably from about 1.4 to about 1.7 wt % cubic carbides of the metalsTa and Nb and WC as the remainder with a content of Ti on a levelcorresponding to a technical impurity with an average grain size of theWC in the range of from about 1.5 to about 2.5 μm, preferably about 1.8μm, a hardness of from about 1500 to about 1600 HV, a CW-ratio of fromabout 0.84 to about 0.94, preferably from about 0.86 to about 0.91, andbefore coating an edge radius of from about 20 to about 45 μm,preferably about 35 μm is coated with

a first (innermost) layer of TiC_(x)N_(y)O_(z) with x+y+z=1, preferablyz<0.5, with a thickness of from about 0.1 to about 2 μm, and withequiaxed grains with size less than about 0.5 μm using knownCVD-methods.

a layer of TiC_(x)N_(y)O_(z) with x+y+z=1, preferably with z=0 and x>0.3and y>0.3, with a thickness of from about 2 to about 10 μm, preferablyabout 4-7 μm, with columnar grains and with a diameter of about lessthan about 5 μm, preferably less than about 2 μm, deposited either byMTCVD-technique (using acetonitrile as the carbon and nitrogen sourcefor forming the layer in the temperature range of 700-900° C.) or byhigh temperature CVD-technique (1000-1100° C.), the process conditionsbeing selected to grow layers with columnar grains, that is generallyhigh process pressure (0.3-1 bar). However, the exact conditions dependto a certain extent on the design of the equipment used and are withinthe purview of the skilled artisan.

a layer of TiC_(x)N_(y)O_(z) with x+y+z=1 with z<0.5, preferably z>0.1,with a thickness of from about 0.1 to about 2 μm and with equiaxed orneedlelike grains with size less than about 0.5 μm, using knownCVD-methods, this layer being the same as or different from theinnermost layer.

a layer of a smooth textured α-Al₂O₃ layer with a thickness of fromabout 2 to about 10 μm, preferably from about 3 to about 6 μm, and asurface roughness (Ra) of less than about 0.3 mm over a measured lengthof 0.25 mm deposited according to U.S. Pat. No. 5,487,625, U.S. Pat. No.5,851,687 or U.S. Pat. No. 5,766,782 and preferably

a further layer from about 0.5 to about 1.0 μm thick layer of CVD- orPVD-TiN. This outermost layer of TiN has a surface roughness Rmax<0.4 μmover a length of 10 μm.

The smooth coating surface is obtained by a gentle wet-blasting of thecoating surface with fine grained (400-150 mesh) alumina powder or bybrushing the edges with brushes based on e.g. SiC as disclosed e.g. inU.S. Pat. No. 5,861,210 if present, a TiN-layer reduced in thicknessover the edge line to 50-90% of the thickness on the rake face.

When a TiC_(x)N_(y)O_(z) layer with z>0 is desired, CO₂ and/or CO isadded to the reaction gas mixture.

The invention also relates to the use of a cutting tool insert accordingto above for side and face milling of rolled low alloyed steel at lowand moderate cutting speeds i.e. less than about 500 m/min.

The invention is additionally illustrated in connection with thefollowing Examples which are to be considered as illustrative of thepresent invention. It should be understood, however, that the inventionis not limited to the specific details of the Examples.

EXAMPLE 1

Cemented carbide milling inserts of special shape 32×20×8 mm inaccordance with the invention with the composition 7.6 wt-% Co, 1.25wt-% TaC, 0.30 wt-% NbC and WC as balance with average grain size of 1.8μm, with a binder phase alloyed with W corresponding to a CW-ratio of0.87, and an edge radius of 35 μm were coated with a 0.5 μm equiaxedTiCN-layer followed by a 5 μm thick Ti(C,N)-layer with columnar grainsby using MTCVD-technique (process temperature 850° C.). In subsequentprocess steps during the same coating cycle, a 1 μm thick layer withequiaxed grains of TiC_(x)N_(y)O_(z) (approx. x=0.6, y=0.2 and z=0.2)was deposited followed by a 4 μm thick layer of (012)-textured α-Al2O3deposited according to conditions given in U.S. Pat. No. 5,487,625.XRD-measurement showed a texture coefficient TC(012) of 1.5. Aftercoating, the inserts were smoothed using a nylon straw brush containingSiC grains. Examination of the brushed inserts in a light opticalmicroscope revealed that the outermost TiN-layer had been somewhatreduced in thickness.

EXAMPLE 2

Chamfer milling of low alloyed rolled steel plates in low carbon steelX70 was performed under the following conditions:

Machine: MFL Austria

Operation: Chamfer milling under dry conditions.

Work piece: Steel plates 4×12 m in 25 mm thickness.

Milling cutter: Böhlerite special cutter of diameter 800 mm.

RPM: 120 r/min

Cutting speed: 300 m/min

Feed rate/tooth: 2.5-3.0 mm

Radial depth of cut: 25 mm

Insert style: 48 pcs of special type 32×20×8

Grade 1: Inserts according to example 1.

Grade 2: Inserts from competitor A

Grade 3: Inserts from competitor B

Tool life criterion: Surface finish.

Result: Tool life number of plates Grade 1 Grade 2 Grade 3 InventionPrior art Prior art 125 plates 78 Plates 74 Plates

It is apparent that 60% better tool life in number of plates compared toprior art is obtained.

Although the present invention has been described in connection with apreferred embodiment thereof, it will be appreciated by those skilled inthe art that additions, deletions, modifications, and substitutions notspecifically described may be made without departing from the spirit andscope of the invention as defined in the appended claims.

1-8. (canceled)
 9. A method of manufacturing a metal workpiece with acutting tool insert including a cemented carbide body and a coating,said cemented carbide body comprising WC, from about 7.3 to about 7.9wt-% Co and from about 1.0 to about 1.8 wt-% cubic carbides of Ta andNb, a highly W-alloyed binder phase with a CW-ratio of from about 0.86to about 0.94, and an edge radius of from about 20 to about 45 μm, saidcoating comprising a first (innermost) layer of TiC_(x)N_(y)O_(z) with athickness of from about 0.1 to about 2 μm, and with equiaxed grains withsize less than about 0.5 μm, a layer of TiC_(x)N_(y)O_(z) with athickness of from about 2 to about 10 μm with columnar grains with adiameter of less than about 5 μm, a layer of TiC_(x)N_(y)O_(z) with athickness of from about 0.1 to about 2 μm and with equiaxed orneedlelike grains with size less than about 0.5 μm, and an outer layerof a smooth, textured, finegrained α-Al₂O₃ layer with a thickness offrom about 2 to about 10 μm, the method comprising: side and facemilling the metal workpiece at low or moderate cutting speeds.
 10. Themethod of claim 9, wherein the metal workpiece is formed of rolled lowalloyed steel.
 11. The method of claim 9, wherein the metal workpiece isa plate.
 12. The method of claim 11, comprising manufacturing a tubefrom the milled plate.
 13. The method of claim 1, wherein the α-Al₂O₃layer has a texture in the (104)-direction with a texture coefficientTC(104) larger than 1.3.
 14. The method of claim 1, wherein the α-Al₂O₃layer has a texture in the (110)-direction with a texture coefficientTC(110) larger than 1.3.
 15. The method of claim 1, wherein the cuttingtool insert includes from about 0.5 to about 1.0 μm thick layer of TiNhaving a surface roughness R_(max)<0.4 μm over a length of 10 μm andreduced in thickness over the edge line to from about 50 to about 90% ofthe thickness on the rake face.
 16. The method of claim 1, wherein thecemented carbide includes from about 1.4 to about 1.7 wt-% carbides ofTa and Nb.
 17. A method of manufacturing a metal workpiece with acutting tool insert, the cutting tool insert including a cementedcarbide body and a coating, wherein said cemented carbide body includesWC, from about 7.3 to about 7.9 wt-% Co and from about 1.0 to about 1.8wt-% cubic carbides of Ta and Nb, a highly W-alloyed binder phase with aCW-ratio of from about 0.86 to about 0.94, and wherein said coatingincludes a first (innermost) layer of TiC_(x)N_(y)O_(z) with a thicknessof from about 0.1 to about 2 μm, and with equiaxed grains with size lessthan about 0.5 μm, a second layer of TiC_(x)N_(y)O_(z) with a thicknessof from about 2 to about 10 μm with columnar grains with a diameter ofless than about 5 μm, a third layer of TiC_(x)N_(y)O_(z) with athickness of from about 0.1 to about 2 μm and with equiaxed orneedlelike grains with size less than about 0.5 μm, an outer layer of asmooth, textured, finegrained α-Al₂O₃ layer with a thickness of fromabout 2 to about 10 μm, and a further layer of TiN having a surfaceroughness R_(max)<0.4 μm over a length of 10 μm, having a thickness on arake face of from about 0.5 to about 1.0 μm and having a reducedthickness over an edge line of from about 50 to about 90% of thethickness on the rake face, the method comprising: side and face millingthe metal workpiece with the cutting tool insert.
 18. The method ofclaim 17, wherein side and face milling is at a cutting speed of lessthan about 500 m/min.
 19. The method of claim 17, wherein side and facemilling is at a cutting speed of 1 about 300 m/min to about 500 m/min.20. The method of claim 17, wherein the cutting tool insert is achamfering cutting tool insert.
 21. The method of claim 17, wherein themetal workpiece is formed of rolled low alloyed steel.
 22. The method ofclaim 17, wherein the metal workpiece is a plate and the methodcomprises manufacturing a tube from the milled plate.
 23. The method ofclaim 17, wherein the α-Al₂O₃ layer has a texture in the (012)-directionwith a texture coefficient TC(012) larger than 1.3.
 24. The method ofclaim 17, wherein the α-Al₂O₃ layer has a texture in the (104)-directionwith a texture coefficient TC(104) larger than 1.3.
 25. The method ofclaim 17, wherein the α-Al₂O₃ layer has a texture in the (110)-directionwith a texture coefficient TC(110) larger than 1.3.
 26. The method ofclaim 17, wherein the cemented carbide contains from about 1.4 to about1.7 wt-% carbides of Ta and Nb.
 27. The method of claim 17, wherein theinsert has an edge radius of from about 20 to about 45 μm beforecoating.
 28. The method of claim 17, wherein said edge radius is about35 μm.
 29. The method of claim 17, wherein said cemented carbide bodycomprises about 7.6 wt-% Co.
 30. The method of claim 17, wherein anaverage grain size of the WC is in a range of from about 1.5 to 2.5 μm.31. The method of claim 17, wherein said CW-ratio is from about 0.86 toabout 0.91.
 32. The method of claim 17, wherein the thickness of thesecond layer of TiC_(x)N_(y)O_(z) is from about 4 to about 7 μm.
 33. Themethod of claim 17, wherein the thickness of the outer layer of α-Al₂O₃is from about 3 to about 6 μm.
 34. The method of claim 17, wherein atexture coefficient of the α-Al₂O₃ layer for the set of (012), (104) or(110) crystal planes is larger than 1.5.